Motor-Sparing Regional Anesthesia for Knee Surgery: Current Evidence on Adductor Canal, IPACK, and 4-in-1 Blocks

Abstract

Background: Regional anesthesia techniques play an important role in perioperative pain management for knee surgery by providing effective analgesia while preserving motor function and facilitating early mobilization. The adductor canal block targets mainly the saphenous nerve and the nerve to vastus medialis, providing sensory analgesia to the anterior and medial aspects of the knee with relative preservation of quadriceps strength. However, its analgesic coverage of the posterior knee capsule may be inadequate. The infiltration between the popliteal artery and the capsule of the knee block was therefore developed to selectively anesthetize the terminal articular branches supplying the posterior capsule without significantly affecting the major motor branches of the tibial and common peroneal nerves. Combining the adductor canal block with the IPACK block can provide more comprehensive anterior and posterior knee analgesia, reduce opioid requirements, and support early ambulation. The modified 4-in-1 block is a more recent ultrasound-guided, single-injection technique designed to target the saphenous nerve, nerve to vastus medialis, posterior branch of the obturator nerve, and articular branches of the sciatic nerve. It aims to provide broad sensory blockade while preserving quadriceps motor function. This mini-review describes the relevant anatomy, indications, techniques, advantages, limitations, contraindications, and potential complications of the adductor canal, IPACK, and modified 4-in-1 blocks. These motor-sparing techniques represent valuable components of multimodal analgesia and Enhanced Recovery After Surgery protocols for total knee arthroplasty and other major knee procedures. Postoperative pain following knee surgery may delay mobilization, increase opioid consumption, impair rehabilitation, and reduce patient satisfaction. Motor-sparing ultrasound-guided regional anesthesia techniques have therefore been developed to provide effective pain relief without causing significant quadriceps weakness. Adductor canal block provides mainly anterior and medial knee analgesia, whereas the IPACK block targets posterior capsular pain. The modified 4-in-1 block was introduced as a single-injection alternative capable of covering several major sensory contributors to the knee joint while preserving motor function.